Flooding along the Reedy River through the west end section of downtown Greenville, South Carolina, on 29 July 2004.

Author's Note: The following report has not been subjected to the scientific peer review process.

1.  Introduction

A record-setting flash flood developed over part of the Greenville, South 
Carolina, metro area during the morning of Thursday, July 29, 2004.  When 
the event ended, 6 to 8 inches of rain had fallen just east of Berea, a 
northwestern suburb, and the Reedy River through downtown Greenville 
crested 9 ft above flood stage, its highest level since 1908.

2.  Meteorological Setting

Scattered rain showers began developing across upstate South Carolina
in the pre-dawn hours of July 29, 2004.  The western Carolinas had been 
in a persistent upslope flow regime for 24 hours, characterized by low-
level easterly and southeast flow off the Atlantic Ocean.  This pattern 
typically results in development of showers across the northern tier of 
upstate South Carolina and parts of western North Carolina with an east 
or southeast aspect, and in that regard, this meteorological event was 
fairly common.  It is not unusual in such a synoptic setup to have 
showers and thunderstorms remain stationary.  However, recent history 
had shown a tendency for cells to anchor along the Blue Ridge Escarpment
(the northeast-to-southwest oriented rapid rise in elevation marking the 
transition from the Piedmont to the Blue Ridge Mountains), especially 
when upper level flow is weak as it was July 29th.

Aside from upslope flow, a number of other factors contributed to this 
extreme rainfall event.  At the surface, a frontal boundary was lifting 
slowly northward.  This boundary, which had passed over the region earlier 
in the week, was retreating ahead of an upper level trough that was 
digging to the southeast from the northern plains.  This boundary 
contributed in at least two ways to the potential for extreme rainfall; 
it served as a convergence mechanism, and it gave an upslope orientation 
to the low level flow.  The surface front separated very moist air, with 
surface dewpoints in the lower to middle 70s, from relatively drier air 
across our northern zones, where dewpoints were in the lower to middle 60s.

The flow aloft was weak, but upper air analysis and water vapor imagery 
showed a short wave approaching from the west.  The 850 mb analysis at 
1200 UTC (8:00 a.m. EDT)Thursday indicated 850 mb dewpoints of 14 OC to 
16 OC over all of the southeast states, with trajectories pointing to a 
continued influx of very moist air into the forecast area.  Soundings at 
1200 UTC showed precipitable waters ranging from 1.52 inches at Peachtree 
City, Georgia (FFC), to 0.96 inches at Blacksburg, Virginia (RNK), and the 
LAPS sounding for Greenville at 1200 UTC indicated precipitable water of 
1.63 inches.

3.  Chronology of the Flood

By 1240 UTC, showers around Greenville had merged to form a small 
convective cluster centered near Berea.  Looping of the KGSP radar 
reflectivity imagery shows the cells merging into a stationary cluster 
about 6 miles wide (Fig. 1).  Low level inflow into the system was also 
evident.  The NWS LARC gage on the Reedy River off Westfield Street in 
downtown Greenville is programmed to call WFO GSP whenever the stage at 
that location reaches 6.0 feet, which it did at 1236 UTC.  It rose 
rapidly to 7.5 ft. at 1243 UTC.

Figure 1.  KGSP radar composite reflectivity at 1131 UTC on 29 July 2004.  
Click on the image to launch a 13-frame Java loop of composite reflectivity 
from 1131 UTC to 1728 UTC.

Radar rainfall estimates at that time were around two inches per hour just 
east of Berea, on the northwest side of Greenville.  A Flood Statement was 
issued for Greenville and eastern Pickens counties at 1253 UTC, indicating 
that flood warnings may be required.  The Reedy River gage in Greenville 
reached flood stage of 8 ft just before 1300 UTC.  At this level flooding 
begins in Cleveland Park, which is a common occurrence and does not, in 
itself, warrant a flood warning.  However, the Reedy River had risen more 
than 5 ft between 1200 UTC and 1300 UTC and the rise was expected to 
continue as the convective cluster remained stationary over the headwaters. 
A Flash Flood Warning was issued at 1304 UTC indicating that the river 
would crest well above flood stage.  A call was made to Greenville County 
Emergency Management at 1310 UTC to advise them of the situation and to 
solicit information.  At that time, no flooding had yet been reported.

The first report of actual flooding away from flood-prone Cleveland Park 
was received by WFO GSP at 1353 UTC.  The Parker District Fire Department 
reported Lewis Road and Old Cedar Lane Road closed, with evacuations 
underway for homes off Lily Street in Berea, where the Long Branch had 
left its banks.  Water completely covered yards of homes closest to the 
creek.  A shelter had been opened at a local church for the evacuees.  An 
Amateur Radio operator reported an old fishing lake, off Lily Street near 
Lions Club Drive and Lora Lane, had overtopped its rim and he feared the 
dam might break with the flow of water coming out of the lake.  In addition, 
urban flooding was becoming severe on some streets, with road closures on 
Cedar Lane Road, Pettis Road, and much-traveled White Horse Road.  This 
information was included in the follow-up Flash Flood Statement, issued 
at 1437 UTC.

Calls continued to be made to the downtown Reedy River gage.  At 1439 UTC, 
the river level was 11.36 feet; at 1506 UTC, the stage had climbed to 
12.21 feet.  New flooding reports arrived, including stalled vehicles in 
flood waters at Cherrydale Point, a major commerce hub, and water on Lily 
Street was up to the roofs of some homes along Long Branch.  Evacuations 
continued and Greenville County Emergency Management reported several swift 
water rescues.  Flooding was reported in buildings on the campus of Furman 
University.  The Flash Flood Warning for Greenville County was extended from 
1600 UTC until 1900 UTC.

In the meantime, the convective cluster that had been nearly stationary 
over the headwaters of the Reedy River for three hours finally began to 
weaken on its westward edge as the system expanded north and east.  This 
shift resulted in the heavy rain axis moving to the headwaters of one of 
Greenville County's other flood-prone creeks, Brushy Creek.  Up to this 
point, heavy rain had been concentrated over west central Greenville 
County, along with a brief but heavy downpour over downtown Greenville 
around mid morning.  As heavy rain moved over the headwaters of Brushy 
Creek, on Greenville's east side, the NWS gage at Del Norte rose from 0.8 ft
at 1500 UTC to 5.8 ft at 1700 UTC.  The Reedy River, meanwhile, continued 
its rapid rise toward a crest of historical proportions, reaching 13.0 ft
at 1530 UTC and 16.1 ft. at 1626 UTC.

By 1730 UTC, rain had ended over the Reedy River basin.  Radar estimates 
indicated storm total rainfall of 6 to 8 inches over the headwaters; an 
automated gage to the west of the radar-estimated maximum, measured 
3.91 inches of rain.  Reports collected after the storm confirmed that the 
maximum rainfall was about 8 inches.  The Reedy River rose to its second 
highest level ever recorded by 1700 UTC, 16.84 feet, nearly 9 feet above 
flood stage.  At that point the gage reached its maximum recording level 
and communications were lost.  A post storm survey revealed that the water 
continued to rise and reached a depth of 19 ft 2 in, which completely 
submerged the gage.

Heavy rain continued into early afternoon over headwaters of Brushy Creek.  
NWS personnel checked the Del Norte gage and observed the flooding there.  
Brushy Creek at Del Norte crested at 8.55 feet shortly before 1900 UTC.
By this time, however, an outflow boundary emerged from the thunderstorm 
complex and the system finally weakened as it drifted to the east.  Rain 
ended over Greenville County by 1930 UTC.  However, radar showed that 
additional showers and thunderstorms had developed southeast of Greenville 
County, and they were heading toward the northwest.  The location and 
movement of these storms indicated they might affect locations still 
experiencing flooding by early evening.  A Flood Warning was issued for 
Greenville County at 1900 UTC with the anticipation that flood waters in 
Berea and west Greenville might not recede significantly by early evening, 
and also taking into account the slowing rise on Brushy Creek at Del Norte.

By 2045 UTC, when a Flash Flood Statement for Greenville County was issued, 
flood waters had receded at Del Norte; the creek stage was down to 7.36 ft. 
Emergency Management confirmed that numerous flooded roads still existed 
in and around Berea.  Another gage on the Reedy River, 6 miles downstream 
from downtown Greenville and adjacent to Interstate 85 mile marker 46, 
showed a rise to over 11 feet in less than 2 hours' time.  This confirmed 
that the flood crest was progressing down the Reedy, with the expectation 
that flood conditions may reach Fork Shoals in the evening.

The upslope-induced convection that developed southeast of Greenville County 
was showing no signs of weakening as evening approached, and it was drifting 
toward Greenville County.  A Flood Watch was posted for many upstate South 
Carolina and western North Carolina counties at 2150 UTC.  As the Flood 
Warning expiration time approached, no rain showers were occurring in 
Greenville County, but there was concern about the precipitation approaching 
from the southeast.  Calls to Emergency Management confirmed that despite 
the fact that several hours had passed since rainfall ended in the vicinity 
of Berea, many roads were still closed.  The decision was made to issue a 
Flood Warning at 2200 UTC, valid until 0400 UTC on 30 July.

Additional Flood Statements were issued at 0015 UTC, 0225 UTC, and 0033 UTC 
on 30 July, each indicating improving road conditions and receding water 
levels.  By midnight, the flood event was over.  The expected redevelopment 
of heavy rain as convection moved up from the southeast, which was the basis 
for the Flood Watch, did not occur.  Cells weakened as they entered the more 
stable air from the earlier convection over Greenville County.  Moderate to 
heavy rain did occur to the east in Spartanburg County, and in the southern 
mountains of North Carolina.

A post storm survey indicated unofficial totals of about 8 inches over the 
headwaters of the Reedy River (Fig. 2). 

Figure 2.  Estimated total rain accumulation (top) and observed rainfall 
(bottom) across Greenville, South Carolina, on 29 July 2004.

4.  Summary 

No deaths or serious injuries resulted from the flood.  At least 75 people 
were rescued from flooded vehicles, homes, and businesses.  Damage to roads 
and bridges was estimated at $5.8 million.  Approximately 30 homes were 
destroyed and another 100 homes and several businesses sustained significant 
flood damage.

Acknowledgements

Patrick Moore converted the original document into the standard web 
page format.